Humans and flies display a wide variety of genetic defects affecting the eye. Our goal is to elucidate the functions of genes expressed in the human retina by using Drosophila as a model system. We will isolate human genes with homology to Drosophila eye genes, and Drosophila homologs of human genes involved in retinal disease, and use them for functional studies in Drosophila. A set of previously isolated eye-specific Drosophila cDNAs will be used to isolate potential functional human retinal cDNA homologs. The Drosophila cDNAs include several with known sequence homology to human eye genes, such as arrestin and rhodopsin, as well as others of novel sequence. Mutations will be induced in the fly genes corresponding to the Drosophila eye cDNAs, and the resultant phenotypes characterized for anatomical and functional defects in the retina and visual transduction pathways. We have also identified other Drosophila genes based on striking defects in retinal differentiation, or expression patterns of interest to visual system development or function. These genes are currently being cloned in our laboratory, and will also be used to isolate candidate human homologs. To test whether a putative human homolog expresses a similar function in the fly, we win attempt to rescue the fly mutant phenotype with the human cDNA. This will be done by constructing hybrid genes, in which Drosophila promoter sequences are linked to the protein-encoding regions of the human homologs. These constructs will be tested for gene and protein expression in Drosophila tissue culture cells, then introduced into the Drosophila germ line by P element-mediated transformation, and analyzed for expression in the fly. Partial or full rescue of the phenotype will be evidence for conservation of function. This methodology will be tested by using human rhodopsin to rescue the phenotype of the Drosophila rhodopsin mutant, hinae. We will also search for Drosophila homologs of the human retinoblastoma gene, for which a clone is available. Drosophila homologs of the gene will be searched for by low stringency hybridization and PCR amplification of regions of the gene conserved through vertebrate evolution. The function will be investigated by the molecular and genetic methodologies available in Drosophila.